This invention relates to a method for supplying a glass molding material to molds and an apparatus used for this method. Moreover, this invention relates to a method for manufacturing glass optical elements including glass optical elements such as high precision lenses using the invented method not requiring grinding and polishing after press molding. Particularly, this invention relates to a method for manufacturing, with high productivity, glass optical elements having a higher surface precision.
Various molding methods for optical glass elements such as high precision lenses, using precisely fabricated molds made of a mold material, which can be finished to an optical surface, to which softened glass does not adhere, and which does not require grinding or polishing after press molding, have been developed recently. To obtain a required lens, the lens has to satisfy the specification such as lens thickness, outer diameter, eccentricity, as well as of surface shape precision and surface quality (smoothness on the surface). It is better for such a lens to have a good internal quality such as good refractive index and permeability as a matter of course.
To run such a molding method for glass optical elements as business, how much productivity would be gained may be a serious problem. That is, it is critical whether many glass optical elements can be produced in a short period.
One means to improve the productivity is to fabricate plural glass material pieces in parallel, and another means is to shorten the fabrication time for one cycle. Various improved methods have been proposed, respectively. Shortening the fabrication time for one cycle requires shortening heating and cooling periods of the molds, and therefore, various ideas are made to the glass material during molding and the temperature condition among the molding conditions.
For example, Japanese Unexamined Patent Publication No. 7-10,556 (hereinafter referred to as xe2x80x9cRelated art No. 1xe2x80x9d) describes a method for press-molding a glass material having a viscosity in a range of 107 to 109 poises with molds heated at a temperature that the glass material indicates a viscosity of 1010 to 1012 poises. Japanese Unexamined Patent Publication No. 9-12,317 (hereinafter referred to as xe2x80x9cRelated art No. 2xe2x80x9d) describes a method for press-molding a glass material having a viscosity in a range of 105.5 to 109 poises with molds heated at a temperature that the glass material indicates a viscosity of 108 to 1012 poises (provided that the temperature of the molds is lower than that of the glass material).
Each method shortens the cycle time by shortening times for increasing and decreasing temperatures where the temperature of the mold is not raised more than a necessary temperature.
Thus, a method for molding glass optical elements, such as high precision lenses, using molds made from a precisely fabricated mold material, to which softened glass does not adhere and which can be finished to an optical surface, has drawn attentions recently and been developed in a various way.
Moreover, in each method, to prevent the molding surface of the molds from becoming impaired, the glass material heated and softened at a place other than the molds is transferred into the molds before molding and is then molded. For example, the glass molding material pieces are transferred above lower molds of the molds in a form of spherical or xe2x80x9cmarblexe2x80x9d (slightly flatted spherical) shaped preforms by means of floating plates or sucking pads, and are dropped on the molds to be supplied to the molds.
For example, Japanese Unexamined Patent Publication No. 6-340,430 discloses a method transferring molten glass by means of floating plates, made of separable plates horizontally openable, which blow gas from porous member surfaces and supplying the glass to the molds by opening the separable plates over the molds.
Japanese Unexamined Patent Publication No. 8-133,758 discloses a method for supplying glass preforms to molds by dropping the heated, softened glass preforms where the glass preforms are floated, using a floating jig having at least one fine hole for supplying air flow to the bottom thereof and having an opening smaller than, equal to, or larger than the diameter of the glass preforms, by air flow from the fine hole to heat and soften the preforms, or where the glass preforms are softened by heating while floated, using a porous floating jig having a spherical surface close to the curvature of the outer diameter of the glass preform or a flat surface, by air flow from the porous material.
Japanese Unexamined Patent Publication No. 8-259,242 discloses a method for supplying glass preforms by dropping the heated, softened glass preforms where the glass preforms softened by heating while rotatively floated, using a floating jig formed in having a trumpet-shaped upward opening, by air flow blowing out of plural fine holes arranged under a portion around the center of the jig.
However, when the glass molding material is spontaneously dropped to be supplied to the molds (lower molds), the following problems are raised depending on shapes or sizes (weights) of the glass molding materials. For example, a relatively small glass molding material may not drop onto the molding surface of the lower molds but may come out of the molds due to conditions of air flow during the drop or contacts with the floating plates or the like. In the case of an aspherical glass material, the position of the material may shift from the center of the molding surface even if dropped on the lower mold, and if molding is made under such a state, the molding material may not spread evenly in the molds, thereby generating irregular thicknesses and producing defective articles in which the molding material is protruded. Particularly, the glass preform may be rotated or slightly vibrated up and down and right and left while floating by air flow, and therefore, when such a glass preform is dropped, the glass preform is in an unstable state at a time that the preform starts dropping. Therefore, in such cases, the above problem easily occurs.
The object of the invention is to provide a method and an apparatus capable of preventing a glass molding material from jumping out of molds during dropping of the material when the glass molding material is supplied to the molds by dropping of the material.
It is another object of the invention to provide a method and an apparatus capable of positioning the glass molding material at substantially a center of a molding surface of a lower mold when the glass molding material is supplied to the molds by dropping of the material.
It is a further object of the invention to provide a manufacturing method for glass optical elements preventing a glass molding material from jumping out of a mold and preventing defective articles from being generated in utilizing the above method.
This invention is to provide a method for supplying a glass molding material (hereinafter referred to as xe2x80x9cSupplying method No. 1xe2x80x9d) by dropping the glass molding material downward onto a molding surface of a lower mold of a mold constituted of an upper mold and the lower mold, comprising the steps of using a guide means for dropping the glass molding material and providing the guide means at a position making the glass molding material drop onto a molding surface of the lower mold.
This invention is also to provide a method for supplying a glass molding material (hereinafter referred to as xe2x80x9cSupplying method No. 2xe2x80x9d) onto a molding surface of a lower mold of a mold constituted of an upper mold and the lower mold, characterized in correcting a position of the glass molding material so that a vertical center of the glass molding material and a center point of a molding surface substantially coincide with each other, after the glass molding material is supplied onto the molding surface of the lower mold.
This invention is further to provide a guide means used in a method for supplying a glass molding material by dropping the glass molding material downward onto a molding surface of a lower mold of a mold constituted of an upper mold and the lower mold, characterized in having a guide portion forming a dropping passage of the glass molding material and allowing the glass molding material to be dropped.
This invention is yet further to provide a position correcting means used for a method for correcting a position of a glass molding material to be supplied onto a molding surface of a lower mold of a mold constituted of an upper mold and the lower mold, characterized in having a glass molding material contact portion for transferring the glass molding material by contacting to the glass molding material, wherein the glass molding material contact portion has a ring shaped edge of an opening or projecting portions arranged coaxially.
This invention relates to a manufacturing method for glass optical elements characterized in press-molding a glass molding material supplied onto a molding surface of a lower mold in utilizing Supplying method No. 1 or Supplying method No. 2 for the glass molding material according to the invention.